1. Technical Field
The present invention relates to a method for manufacturing an electrophoretic display apparatus.
2. Related Art
It is generally known that applying an electric field to a liquid dispersion system containing dispersed fine particles makes the fine particles move (migrate) in the liquid through the action of Coulomb force. This phenomenon is referred to as electrophoresis, and recently electrophoretic display apparatuses, which make use of electrophoresis to display some desired information (image), have attracted public attention as a new generation of display apparatuses. The features of electrophoretic display apparatuses include the ability to hold the displayed information even with no voltage applied, a wide viewing angle, a high-contrast display capability with low power consumption, and so forth.
Furthermore, electrophoretic display apparatuses, which are non-luminous devices, are friendlier to eyes than cathode ray tubes (CRTs) and other self-luminous devices. A known constitution of electrophoretic display apparatuses is that in which a pair of substrates have the space therebetween divided by partitions into several subspaces (hereinafter also referred to as cells) and the cells are sealed after being loaded with dispersion liquid (containing charged particles and a dispersion medium) (e.g., see JP-A-2008-107484). Another known constitution is that in which a fluorine-containing solvent is used as the dispersion medium of the dispersion liquid (see JP-T-2006-517038). Each cell has an opening through which it is loaded with the dispersion liquid. After the cells are loaded with the dispersion liquid, the openings are sealed with a sealing coating.
Using a fluorine-containing solvent as the dispersion medium will prevent the dispersion liquid and the sealing coating from being mixed (i.e., blended). This is because fluorine-containing solvents have a low affinity with both hydrophilic materials and lipophilic ones and thus are substantially immiscible with them. Furthermore, the dispersion medium can be a solvent having a higher specific gravity than that of the sealing coating; this will prevent physical mixing of the sealing coating and the dispersion liquid.
As mentioned above, the technology disclosed in JP-T-2006-517038 uses a fluorine-containing solvent as the dispersion medium. This will prevent the blending of the dispersion liquid and the sealing coating. However, fluorine-containing solvents are difficult to synthesize, and materials for them are expensive. Worse yet, there are only a few kinds of fluorine-containing solvents available, limiting the choice of solvent.
Thus, the present inventor has been focusing on hydrocarbon solvents, which are available at affordable prices. Hydrocarbon solvents are easier to manufacture than fluorine-containing ones; for example, the manufacturing cost of the former is one digit smaller than the latter's. Using a hydrocarbon solvent as the dispersion medium will therefore reduce the manufacturing cost of an electrophoretic display apparatus.
However, the use of a hydrocarbon solvent may cause the blending of the dispersion liquid and the sealing coating. For example, using a lipophilic sealing coating concomitantly with a lipophilic hydrocarbon solvent may result in the sealing coating at least in part dissolved in the dispersion liquid and the sealing coating and the dispersion liquid being blended, leading to incomplete sealing of the dispersion liquid. The present inventor actually made a coating of such a polyurethane-based acrylic resin as specified in JP-T-2006-517038 and IRGACURE® 907 and attempted to seal a (fluorine-free) hydrocarbon solvent with it, but unfortunately the sealing coating and the solvent were blended.
The technology disclosed in JP-T-2006-517038 does not necessitate making the sealing coating from a material substantially immiscible with the dispersion liquid because with this technology the sealing coating and the dispersion liquid will never be blended even if the dispersion liquid loaded in the cells is contaminated by or coated with the sealing coating whether the sealing coating is hydrophilic or lipophilic. On the other hand, using a hydrocarbon solvent as the dispersion medium may cause the sealing coating and the dispersion liquid to be blended and thus poses the problem of the need for making the sealing coating from a material substantially immiscible with the dispersion liquid.